This invention relates to control of particle size of new, improved, hydrophilic, crosslinked polyurethane solid, discrete particles and to a method for their preparation. More particularly, the present invention relates to hydrophilic solid particles prepared from a capped polyoxyethylene polyol reactant having a defined average reaction functionality greater than two and being dissolved in a water-soluble solvent which is then admixed and reacted with large amounts of an aqueous reactant.
Numerous attempts have been made in the prior art to produce hydrophilic polyurethane particles. Typical methods of forming polymeric particles or polymers have been described in the literature. Solution, suspension and emulsion polymerization have been used to form particles of the desired size. Techniques for such preparations are described in The Encyclopedia of Polymer Science and Technology, 1972, John Wiley & Sons, Inc., under the Topics Suspension Polymerization at pg. 552 of Vol. 13 and Ion Exchange Polymers--Synthesis and Characteristics at pg. 700 of Vol. 7. Polymeric powders have also been formed by mechanical working or solution methods as described in the same text under Powder Coatings at pg. 544, Vol. 1, of the 1976 Supplement. The particles can be formed by pelletizing, granulating, spray-drying or chemical precipitation.
The formation of polymer particles in situ having an average diameter in the range 0.1-100 mils by the reaction of prepolymer polyurethanes being added to an aqueous medium is set forth in copending application having Ser. No. 44,808, filed June 1, 1979, assigned to the same assignee and incorporated herein by reference in its entirety. The instant invention sets forth a composition and method of reducing the size of the discrete, solid, hydrophilic crosslinked polyurethane particles formed therein.